This invention pertains generally to the field of hydrogen generation. More specifically, the invention relates to a fuel processor and method for autothermally reforming hydrocarbons to produce hydrogen for fuel cell power generating systems.
Fuel cells electrochemically oxidize hydrogen to generate electric power. Without a hydrogen refueling infrastructure, hydrogen has to be produced from available fuels at the point of use. In remote, distributed, and portable power applications, such fuel cell systems require small, lightweight fuel processors that are designed for frequent start ups and are capable of operating at varying loads.
Two processes are industrially used to generate hydrogen from hydrocarbon fuels. These two processes include the steam reforming process and the partial oxidation reforming process. The steam reforming hydrogen production process is the more commonly used process used to produce hydrogen. This is especially true in the chemical industry. Steam reforming is an endothermic reaction that is typically slow to start up. In steam reforming processes, steam reacts with a hydrocarbon fuel in the presence of a catalyst to produce hydrogen. In steam reforming, the process equipment tends to be heavy and is designed for continuous operation under steady state conditions making such systems unsuitable for applications with frequent load variations such as those for use in transportation applications. Additionally, because of the endothermic nature of the process, steam reforming reactors are heat transfer limited. These attributes of steam reforming processes makes them unsuitable for use in remote, distributed, and portable power applications such as for use in a motor vehicles.
Partial oxidation reforming processes are based on exothermic reactions in which some fuel is directly combusted. In partial oxidation reforming, oxygen reacts with a hydrocarbon fuel in the presence of a catalyst to produce hydrogen. Heat transfer limitations are eliminated in partial oxidation reforming processes due to the exothermic nature of the reaction. Additionally, partial oxidation reforming hydrogen production processes and the equipment used in such processes generally allows for faster start ups compared to steam reforming processes. However, reactors used in partial oxidation reforming processes generally operate at temperatures of from about 1100xc2x0 C. to about 1200xc2x0 C. to prevent coking in the reactor. One disadvantage associated with partial oxidation reforming is that reactor materials capable of operating at the high temperatures of partial oxidation processes must be used. Suitable materials for use in partial oxidation reforming reactors include ceramics. Ceramic reforming reactors are both expensive and difficult to fabricate.
U.S. Pat. No. 5,248,566 issued to Kumar et al. discloses a fuel cell system for use in transportation applications. In the disclosed fuel cell, a partial oxidation reformer is connected to a fuel tank and to a fuel cell. The partial oxidation reformer produces hydrogen-containing gas by partially oxidizing and reforming the fuel with water and air in the presence of an oxidizing catalyst and a reforming catalyst.
U.S. Pat. No. 6,025,403 issued to Marler et al. discloses a process for integrating an autothermal reforming unit and a cogeneration power plant in which the reforming unit has two communicating fluid beds. The first fluid bed is a reformer reactor containing inorganic metal oxide and which is used to react oxygen and light hydrocarbons at conditions sufficient to produce a mixture of synthesis gas, hydrogen, carbon monoxide, and carbon dioxide. The second fluid bed is a combustor-regenerator which receives spent inorganic metal oxide from the first fluid bed and which provides heat to the inorganic metal and balance the reaction endotherm, by combusting fuel gas in direct contact with the inorganic metal oxide producing hot flue gas. In preferred embodiments, steam is also fed to the reformer reactor and a catalyst may be used with the inorganic metal oxide.
U.S. Pat. No. 6,126,908 issued to Clawson et al. and WO 98/08771 disclose an apparatus and method for converting hydrocarbon fuel or an alcohol into hydrogen gas and carbon dioxide. The apparatus includes a first vessel having a partial oxidation reaction zone and a separate steam reforming reaction zone that is distinct from the partial oxidation reaction zone. The first vessel of the apparatus has a first vessel inlet at the partial oxidation reaction zone and a first vessel outlet at the steam reforming zone. The reformer also includes a helical tube that has a first end connected to an oxygen-containing source and a second end connected to the first vessel at the partial oxidation reaction zone. Oxygen gas from an oxygen-containing source can be directed through the helical tube to the first vessel. The apparatus includes a second vessel with both an inlet and outlet. The second vessel is annularly disposed about the first vessel, and the helical tube is disposed between the first vessel and the second vessel and gases from the first vessel can be directed through the second vessel. The temperature in the partial oxidation zone within the apparatus is preferably maintained in the range of from about 950xc2x0 C. to about 1150xc2x0 C.
WO 700/66487 discloses an autothermal reforming system with a reformer reactor, integrated shift beds, preferential oxidation reactor, auxiliary reactor, and system controls. The reformer reactor of the autothermal reforming system is similar to that disclosed in U.S. Pat. No. 6,126,908 issued to Clawson et al. and WO 98/08771 in that it has distinct and separate partial oxidation, steam reforming, low temperature shift, and high temperature shift zones. The exothermic reaction in the partial oxidation chamber is self-sustaining and maintains an operating temperature in the range of from about 700xc2x0 C. to about 1,200xc2x0 C. for an embodiment of a catalyzed partial oxidation chamber or at a temperature of from about 1,200xc2x0 C. to about 1,700xc2x0 C. for an embodiment that uses a non-catalyzed partial oxidation zone.
U.S. Pat. No. 5,458,857 issued to Collins et al. discloses a combined reformer and shift apparatus. The combined reformer and shift reactor comprises a cylindrical reforming chamber arranged within and on the axis of a cylindrical vessel. An annular steam generator is arranged within, and coaxially with the vessel. The steam generator is arranged around the reforming chamber. A plurality of shift reactors extend axially, with respect to the vessel through, through the steam generator. Methane and steam are supplied via helically coiled pipe to the reforming chamber and air is supplied via helically coiled pipe. The methane and steam mixture and air flowing through the pipes are preheated by the reforming chamber product gases flowing in annular passage. The methane is preheated to prevent quenching of the steam in the disclosed apparatus and method of operation. The normal operating temperature in the reforming chamber is 700xc2x0 C. to 1200xc2x0 C. and the low temperature shift reactors are operated at a temperature between 140xc2x0 C. and 250xc2x0 C.
U.S. Pat. No. 5,861,137 issued to Edlund discloses a steam reformer with internal hydrogen purification that include internal bulk hydrogen purification, internal hydrogen polishing to remove trace levels of carbon monoxide and carbon dioxide, an integrated combustion method utilizing waste gas to heat the reformer, efficient integration of heat transfer, and compact design. The steam reformer includes a concentric cylindrical architecture nesting an annular combustion region, an annular reforming region separate from the combustion region, an annular hydrogen transport region, and a cylindrical polishing region. Thus, the reforming apparatus disclosed is similar to other conventional apparatus in having distinct and separate chambers for partial oxidation and steam reforming.
A need remains for a fuel processor that optimizes the production of hydrogen in autothermal reforming processes such that the fuel processor can be manufactured from conventional materials.
The invention provides a fuel processor and a method for generating a H2 rich gas stream.
A method of producing a H2 rich gas stream is provided which includes supplying an O2 rich gas, steam, and fuel to an inner reforming zone of a fuel processor that includes a partial oxidation catalyst and a steam reforming catalyst or a combined partial oxidation and stream reforming catalyst. The method also includes contacting the O2 rich gas, steam, and fuel with the partial oxidation catalyst and the steam reforming catalyst or the combined partial oxidation and stream reforming catalyst in the inner reforming zone to generate a hot reformate stream. The method still further includes cooling the hot reformate stream in a cooling zone to produce a cooled reformate stream. Additionally, the method includes removing sulfur-containing compounds from the cooled reformate stream by contacting the cooled reformate stream with a sulfur removal agent. The method still further includes contacting the cooled reformate stream with a catalyst that converts water and carbon monoxide to carbon dioxide and H2 in a water-gas-shift zone to produce a final reformate stream in the fuel processor.
A preferred method for producing a H2 rich gas stream is provided in which the hot reformate is cooled by directly injecting water into the hot reformate stream. In other preferred methods, the hot reformate stream is at a temperature ranging from about 600xc2x0 C. to about 800xc2x0 C.
Preferred methods are provided in which the catalyst in the inner reforming zone is a combined partial oxidation and steam reforming catalyst. Such preferred catalysts include a transition metal and an oxide-ion conducting portion. The transition metal in such catalysts is selected from platinum, palladium, ruthenium, rhodium, iridium, iron, cobalt, nickel, copper, silver, gold, or combinations of these, and the oxide-ion conducting portion is a ceramic oxide selected from those crystallizing in the fluorite structure for LaGaO3. Still other methods are provided in which the combined partial oxidation and steam reforming catalyst is platinum on gadolinium doped ceria.
A method of producing a H2 rich gas stream is further provided in which cooled reformate stream is at a temperature ranging from about 200xc2x0 C. to about 400xc2x0 C. after cooling in the cooling zone. Still other methods are provided which further include passing the hot reformate gas through an outer reforming zone adjacent to the inner reforming zone. In such methods the outer reforming zone preferably includes a partial oxidation catalyst and a steam reforming catalyst or a combined partial oxidation and steam reforming catalyst such as those described above.
Still further methods for producing a H2 rich gas stream are provided in which the inner reforming zone is formed of stainless steel. In yet other methods, the steam and fuel are supplied to the inner reforming zone through a single pipe as a mixture and the O2 rich gas is separately supplied to the inner reforming zone. In still other methods, the O2 rich gas is supplied to the inner reforming zone through a tube surrounded by the inner reforming zone.
Yet other methods for producing a H2 rich gas stream are provided in which the steam, the fuel, and the O2 rich gas are supplied to the inner reforming zone through a single pipe as a mixture.
In still other methods of producing a H2 rich gas stream also include heating the steam before it is introduced into the single pipe and heating the O2 rich gas before it is introduced into the single pipe. In certain such methods, the steam is heated by passing it through a steam heating zone in the fuel processor, and the O2 rich gas is heated by passing it through an air heating zone in the fuel processor.
Still further methods for producing a H2 rich gas stream are provided in which the fuel has the formula CnHmOp where n has a value ranging from 1 to 20 and is the average number of carbon atoms per molecule of the fuel, m has a value ranging from 2 to 42 and is the average number of hydrogen atoms per molecule of the fuel, p has a value ranging from 0 to 12 and is the average number of oxygen atoms per molecule of the fuel. In such methods, the molar ratio of O2 supplied to the inner reforming zone per mole of fuel is represented by the symbol x and has a value ranging from about 0.5x0 to about 1.5x0 where x0 is equal to 0.312nxe2x88x920.5p+0.5(xcex94Hf,fuel/xcex94Hf,water), n and p have the values described above, xcex94Hf, fuel is the heat of formation of the fuel, and xcex94Hf, water is the heat of formation of water. Still other such methods are provided in which the molar ratio of steam supplied to the inner reforming zone per mole of fuel is a value ranging from about 0.8(2nxe2x88x922xxe2x88x92p) to about 2.0(2nxe2x88x922xxe2x88x92p).
Yet further methods of producing a H2 rich gas stream are provided in which the sulfur removal agent is zinc oxide whereas in still other methods the catalyst that converts water and carbon monoxide to carbon dioxide and H2 in the water-gas-shift zone comprises a noble metal on ceria where the noble metal is selected from ruthenium, rhodium, palladium, platinum, and combinations of these metals.
Additional methods of producing a H2 rich gas stream are provided which include supplying the final reformate stream to a preferential oxidation unit that includes a catalyst that preferentially oxidizes carbon monoxide to carbon dioxide.
Still another method of producing a H2 rich gas stream is provided that includes contacting the cooled reformate stream with at least two different catalysts in at least two different water-gas-shift zones, the at least two different catalysts converting water and carbon monoxide to carbon dioxide and H2 to produce a final reformate stream in the fuel processor.
The invention also provides a fuel processor for generating a H2 rich gas from a fuel. The fuel processor includes an inlet projecting through an exterior housing of the fuel processor attached to a steam line, an O2 rich gas line, and a fuel line; an inner reforming zone including a sidewall, a first end connected to the inlet, a partial oxidation catalyst and a steam reforming catalyst or a combined partial oxidation and steam reforming catalyst, and a second end; an outer reforming zone including the sidewall of the inner reforming zone, an outer sidewall, a first end connected to the second end of the inner reforming zone, and a second end; a cooling zone that includes a first end connected to the second end of the outer reforming zone and a second end; a sulfur removal zone that includes a sulfur removal agent, a first end connected to the second end of the cooling zone, and a second end; and a water-gas-shift zone that includes a catalyst that catalyzes the conversion of carbon monoxide and water to carbon dioxide and H2, a first end connected to the second end of the sulfur removal zone; and a second end connected to an outlet of the fuel processor.
The invention also provides a fuel processor in which the cooling zone includes an injection tube that allows water to be directly injected into the cooling zone. In still other provided fuel processors the outer reforming zone includes a partial oxidation catalyst and a steam reforming catalyst or a combined partial oxidation and steam reforming catalyst.
The invention further provides a fuel processor in which the inner reforming zone includes a combined partial oxidation and steam reforming catalyst comprising a transition metal and an oxide-ion conducting portion such as the catalysts described above.
The invention still further provides a fuel processor in which the sidewall of the inner reforming zone and the outer sidewall of the outer reforming zone are formed from stainless steel.
Still other fuel processors are provided that include a steam heating zone disposed between at least a portion of the outer reforming zone and at least a portion of the water-gas-shift zone while other fuel processors include an air heating zone disposed between at least a portion of the water-gas shift zone and the exterior housing of the fuel processor.
Still other fuel processors are provided in which the sulfur-removal agent comprises zinc oxide while in still other fuel processors the catalyst in the water-gas-shift zone comprises a noble metal on ceria, wherein the noble metal is selected from the group consisting of ruthenium, rhodium, palladium, platinum, and combinations thereof.
Another fuel processor according to the present invention includes: an inlet projecting through an exterior housing of the fuel processor into a mixing zone, the inlet attached to a steam line and a fuel line; an inner reforming zone including a sidewall, a first end connected to the inlet, and a second end; an inner tube attached to an O2 rich gas line and at least partially surrounded by the inner reforming zone; an outer reforming zone including the sidewall of the inner reforming zone, an outer sidewall, a first end connected to the second end of the inner reforming zone, and a second end; a cooling zone including a first end connected to the second end of the outer reforming zone and a second end; a sulfur removal zone including a first end connected to the second end of the cooling zone, and a second end; and a water-gas-shift zone including a first end connected to the second end of the sulfur removal zone, and a second end connected to an outlet of the fuel processor.
The invention further provides a fuel processor such as that described above in which the water-gas-shift zone includes a first water-gas-shift zone and a separate second water-gas-shift zone. The first water-gas-shift zone includes a first end connected to the second end of the sulfur removal zone, and a second end, and the second water-gas-shift zone includes a first end connected to the second end of the first water-gas-shift zone and a second end connected to the outlet of the fuel processor. In still other such fuel processors, the second water-gas-shift zone comprises a cooling tube having an inlet and an outlet and extending through the second water-gas-shift zone.
Fuel processors are also provided in which the inner tube attached to the O2 rich gas line extends into the mixing zone of the fuel processor.
Yet other fuel processor are provided that include a steam inlet that extends through the exterior housing of the fuel processor and is connected to a pipe that extends through the fuel processor to a steam outlet. The steam outlet in such fuel processors is connected to a steam line that is connected to the inlet projecting through the exterior housing and into the mixing zone.
Still other fuel processor according to the invention are providing that have a fuel inlet connected to a fuel line that runs through the fuel processor or around the exterior housing of the fuel processor to a fuel outlet. The fuel outlet of such fuel processors is connected to a fuel line that is connected to the inlet projecting through the exterior housing and into the mixing zone.
Yet another fuel processor is provided in which the cooling zone includes a coiled coolant tube that extends through the cooling zone of the fuel processor.
Still further fuel processors are provided in which the sidewall of the inner reforming zone and the outer sidewall of the outer reforming zone are formed of stainless steel or similar materials of construction.
Further features, and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the appended drawings.